High frequency antenna and transmission line



May l3, 1941. w. R. KOCH 2,241,913

HIGH FREQUENCY ANTENNA AND TRANSMISSION LINE Filed NOV. 10, 1958 3 nventor (Ittorneg Patented May 13, 1941 man we HIGH FREQUENCY ANTENNA AND TRANSMISSION LINE Winfield R. Koch, Haddonfield, N. J., assignor to Radio Corporation of America, a corporation of Delaware 7 Claims.

This invention relates to high frequency antennas and the transmission connected thereto and more particularly to a vertical half-wave high frequency antenna in which the transmission line connected thereto has a negligible radiation factor.

If a vertical half-wave antenna is erected at a considerable distance above the transmitter, it becomes necessary to connect the two by means of a transmission line. It has been found that the transmission line has induced in it currents which are radiated. This radiation takes effect notwithstanding the shielding of the transmission line because the currents in the antenna induce currents in the shielding which currents cause radiation. The additional and undesired radiation interferes with the desired radiation.

Among the objects of this invention is the provision of means for connecting an antenna with a transmitter and at the same time preventing radiation from the connecting means. Another object is the provision of a transmission line for connecting the transmitter to a radiator in such a manner that the transmission line offers low impedance to the currents applied to the radiator and high impedance to the electromotive forces induced in the transmission line. An additional object is to provide means for neutralizing currents induced in a transmission line which connects a transmitter and a radiator.

The invention will be described by referring to the accompanying drawing, in which Figure 1 is a schematic illustration of a vertical antenna and shielded transmission line; Figure 2 is a schematic circuit diagram illustrating one embodiment of the invention; Figures 3 and 4 represent modifications of the invention; and Figure 5 is an elevational view showing one method of mounting the antenna on a supporting mast.

Referring to Fig. 1, if a concentric line I comprising an inner conductor 3 and an outer conductor 5 is connected to a half-wave radiator I, it has been found that the currents in the radiator establish currents in the outer conductor which radiate and thereby cause undesired changes in the pattern of the radiated field. The distribution of the currents affecting the radiated field is represented by the wavy line 9. One of the objects of the invention is to substantially reduce the currents which cause the undesired radiation. This may be accomplished by the arrangement illustrated in Fig. 2. A series of hollow metallic members II are supported by insulators l3 or by an insulating member, as shown in Fig. 5. Within each section of the hollow members, which are preferably a quarter-wave long, are arranged transmission lines l5 which terminate in inductors H. The inductors in each section are mutually coupled I9 to the inductor in the adjacent section. The final or topmost section 2| is connected to the next lower section by an inductor 23 which is mutually coupled to the final inductor in the transmission line.

Currents are applied to the initial section of the transmission line I5 by a suitable transmitter 25. These currents flow through the successive transmission line sections and are finally applied to the two upper most sections which form a half-wave radiator. I The currents in the radiator induce electromotive forces in the lower sections H but since these sections are separated and are of quarter-wave length, their impedance will bevery high and therefore substantially no current will flow in the outer surfaces of the shielding members H. In the arrangement thus described, the current distribution in the radiator and outer surfaces of the shielding line is represented by the line 21. This line indicates that substantially all of the radiation takes place in the half-wave dipole. In some installations, the capacity between the ends of. the adjacent sections may cause a substantial amount of undesirable coupling. This may be eliminated as indicated by the arrangement illustrated in Fig. 3.

In Fig. 3 the supporting sections of the antenna are indicated as concentric lines 29. Each section of the concentric line is preferably one quarter-wave length long. The lines are coupled by transformers 3! which may be tuned by capacitors 33. These capacitors may be connected in series or parallel, as may be required. The undesired capacity between the supporting sections is indicated by the dash line capacitors 35. The reactance of this capacity is neutralized by a shunting inductor 31. In this arrangement the upper radiator is a rod 39 and the lower portion of the radiator may be a concentric member 4!. The radiator members are connected by the secondary 43 of a transformer 45. The primary 4! of the transformer is connected to the upper termination of the transmission line.

In some installations the neutralization of the capacitive reactance between the successive sections may be insufiicient to completely neutralize the coupling between sections. an additional coupling may be used to neutralize. In Fig. 4 one such section is illustrated. The upper and lower sections of a concentric line are indicated by reference numerals 47, 49, respectively. The coupling for the transmission of cur- In such event,

rents to the antenna .is indicated by the transformer 5|. This transformer may include a resonant primary 53 and a resonant secondary 55. The capacity coupling between the adjacent sections of the transmission line is indicated by the dash line capacitor 51. An inductor 59 is connected across the capacitor 51 so that the capacitive reactance is neutralized. A second inductor BI is suitably coupled to the first mentioned inductor 59. The second inductor is connected to the transmission line 49 in such phasal relation as may be necessary to neutralize currents flowing in the supporting sections of the antenna.

As shown in Fig. 5 the several sections of the antenna may be supported on a wooden mast 63. For the sake of simplicity, the antenna sections 65 are shown without the circuit arrangements which have been completely illustrated in Figs. 2, 3 and 4. Likewise, no attempt has been made to show the total number of sections which will vary according to the height of the radiating sections above the transmitter.

Thus the invention has been described as a high frequency antenna system in which the two upper sections form a dipole radiator and in which the lower sections support the radiator.

The lower sections form a transmission line which ofiers low impedance to currents applied to the radiator and very high impedance to currents induced therein by the currents flowing in the radiator. Means have been shown whereby the capacity coupling in the high impedance sections may be neutralized. Means are also provided for neutralizing any undesired currents which tend to flow on the outer surface of the shielding conductors of the transmission line. It should be understood that the invention is not limited to any precise length of line provided the sections are adjusted to offer high impedance to induce currents. It also follows that the radiating sections may be of any appropriate electrical length.

I claim as my invention:

1. A high frequency antenna comprising two quarter wave radiating sections and a plurality of quarter wave transmission line sections all arranged in a straight line, an input coupling means including an impedance connected between said radiating sections, means coupling each of said transmission line sections to each succeeding section. for transferring currents through said transmission line sections, means for coupling the first of said transmission line sections to a power source, and means for coupling the last of said transmission line sections to said input coupling means.

2. An antenna system including in combination, a radiating section and a plurality of quarter wave transmission line sections, means coupling said transmission line sections so that currents may be transmitted therethrough, means for applying said currents to the radiating section at substantially its center, said transmission line sections including undesirable capacity couplings, and means for neutralizing said couplings.

3. An. antenna system including a pair of radiating sections and a plurality of transmission line sections all collinearly arranged, means coupling said transmission line sections for transmitting currents to be radiated to said radiating sections, and means coupling said radiating sections and said transmission line sections, said transmission line sections having an effective length equal to a quarter wave so that they ofier high impedance to electromotive forces induced therein by the currents in the radiating sections.

4. In an antenna system of the character of claim 3 in which the adjacent transmission line sections are coupled by undesirable capacities, means for neutralizing the capacity reactance of said couplings. I

5. In a system of the character of claim 3, means for neutralizing the capacity reactance between adjacent sections of said transmission line, and means for neutralizing the tendency of currents to flow in said adjacent sections.

6. An antenna system including a plurality of substantially coaxially and collinearly arranged quarter wave sections, means coupling said sections for the transmission of currents from the first successively through each of said sections to the last of said quarter wave sections, and means for applying said transmitted currents to the last two sections so that the said last two sections act as a half wave radiator.

7. An antenna system including a plurality of serially arranged quarter wave transmission line sections in non-conductive collinear relation, means coupling the adjacent sections for the transmission of currents therethrough, a quarter wave radiator, and means connecting the last section to said quarter wave radiator so that the last of said sections and said quarter wave radiator form a half wave radiator.

WINFIELD R. KOCH. 

